1. Field of the Invention
This invention relates to a control valve of an exhaust gas recirculation (EGR) apparatus.
2. Prior Art
It is well known that the EGR apparatus controls formation of nitrogen oxides in the combustion chamber by leading part of the exhaust gas from the exhaust line to the suction line through an EGR passage. EGR largely affects the operating characteristics of an engine, and so it becomes necessary to stop EGR in a certain engine condition. Therefore, an EGR valve usually is provided as a control valve in the EGR passage. Deposits are formed by the passage of the exhaust gas, and thus formed deposits cause the recirculating exhaust gas to change its flow characteristic. Particularly, the deposit around the throttling portion of the EGR valve exerts a large influence on the flow characteristic and thus hinders correct EGR control.